Method and apparatus for lapping bores



H. S. INDGE METHOD AND APPARATUS FOR LAPPING BQORES Qct. 31, 1939.

Filed Feb. 5, 1938 JW/ R M/WNW 3 3 m vmll \NZZ? in close precisionlimits.

Patented Oct. 31, 1939.

PATENT OFFICE- 'METHOD AND APPARATUS roa LAPPING BORES Herbert S. Indge,Westboro, Mass., assignor to Norton Company, Worcester, Mass., acorporation of Massachusetts Application February 5, 1938, Serial No.188,897

7 Claims.

One object of the invention is to provide a readily controlled apparatusfor lapping to with- I Another object of the invention is to provide aneconomical and quick method of lapping bores to close precision limits.Another object of the invention is to provide a readilyoontrolledlapping apparatus of the character indicated. Another object of theinvention is to facilitate production of articles which for somerequirement of engineering have to be lapped to fine precision, limits.Other objects will be in part obvious or in part pointed outhereinafter.

The invention accordingly consists in the features of construction,combinations of elements, arrangements'of parts, and in the severalsteps and relation and order of each of said steps to one or more of theothers thereof, all as will be illustratively described herein, and thescope of the application of which will be indicated in the followingclaims. I

The accompanying drawing, in which is illustrated one of many possibleembodiments of the mechanical features of my invention,

Figure 1 is a vertical axial sectional view of a lapping apparatusconstructed in accordance with the invention, together with a Wiringdiagram;

Figure 2 is a horizontal sectional view taken on the line 2-2 of Figure1;

Figure 3 is a horizontal sectional view taken on the line 33 of Figure1;

I Figure 4 is, an isometric view of a lap and a charging plate for thecharging of the lap.

Referring first to Figure 1, the apparatus of the invention is intendedto be applied to a drill press or the like whereby the lapping elementmay be rotated and manually traversed up and down.

The drill press is not shown in detail herein, since any suitable typeof drill press may be used. Such drill press may have a relativelystationary sleeve III in which is journalled a rotatable hollow spindleII. An aperture I2 extending through the spindle II and intersecting itstapered bore I3 provides access for a wedge, not shown, which may beused to remove the shank I4 of the tool which, while the apparatus is inuse, is firmly wedged in the spindle II. I

' The bottom of the shank I4 has a reduced portion I5 transverselythrough which is a pin I 6. This pin I6 seats in a slot I! in a screwthreaded end I8 of a spindle I9. A collar 20 with an annular flange 20ais screwed-onto the top of the spindle I8 and overlaps the pin I6, thusholding the spindle I3 to the shank I4, allowing universal movement ofthe lapping tool. This is in order that the lap may align itself in thebore of the article being lapped.

The spindle I9 has an internal bore 2I from the bottom nearly to thetop, as shown. Fitted on the spindle I9 is an insulating sleeve 22. Thismay be securely attached in place by means of a screw 23. The sleeve 22holds four commutator rings 24, 25, 26 and 21. Four brushes 28, 29, 30and 3I are in engagement with the rings 24, 25', 26 and 21,respectively, and are fastened to an insulating rod 32. The constructionof the brushes may vary widely, one construction being shown in Figure2, according to which as shown each brush has an outer part 33 which hasa bore for the insulating rod 32 and is' clamped to it by means of ascrew 34. The part 33 has a semi-circular cutout fitting one of therings 24 to 21 and an outer half bearing portion 35 is attached to theportion 33 by means of screws 36. This arrangement insures a goodcontact between the brush and the ring at all times and at the same timethere may be enough play so that an undue amount of friction will not bedeveloped.

An internal structure for the support of wires is provided in the bore 2I-. As shown in Figure 1, I provide a long hollow rod of insulatingmaterial 31 having a plurality of enlarged portions 38 which fit thebore.2I. Small bores 39 are pro- 1 vided through the enlarged portions38 to permit the passage of wires. The rod 31 is held to the spindle I9by means of a long metal rod 40 having a head 4I holding a porcelaininsulator 42 to the lower end of the rod 31 and having a screw threadedupper end '43 in screw threaded engagement with the spindle I9.

Insulating sleeves 44 are provided in the wall of the spindle I9 so thatwires can pass therethrough connecting the rings 24, 25, 26 and 21 tothe electric apparatus supported by the spindle I9.

The porcelain insulator 42 has a helical groove 50 in its outer surfacein which is located resistance heating wire 5I. A conductor wire 52connects to the top end of the.wire 5I and also to the ring 24. Aconductor wire 53 connects to the bottom end of the resistance wire 5|and to the ring 21. Referring now to the righthand part of Figure l andthe Wiring diagram, the brushes 28 and 29 are connected to conductors 55and 53 which are connected to power lines 51. A rheostat58 may beinterposed in the conductor 55 as well as an ammeter 59 and 'a switch60. A volt' meter GI may be-connected across the conductors I5, 56 andso also may an incandescent'lamp 62 whereby the operator will know whenthe current is on.

Referring to the lower part of Figure 1, in the interior of theporcelain insulator 52 is a'thermocouple 63. Conductors 64 and 65connect the thermocouple 63 to the rings 26 and 21. conductors 61 and 68connect the brushes 30 and 31 to an ammeter 10. This ammeter 10 measuresthe temperature of the heating unit whi v comprises the porcelaininsulator 42 wound with the resistance wire 5|.

Around the heating unit aforesaid is a cylindrical lapping element 15.This may be of any metal which is readily charged with abrasive. Theupper portion of the lap 15 has an internally threaded taper bore 15.The lower end of the spindle I9 is slabbed off to form an expandingc'ollet 1] having taper sides 18 which may be engaged by a taper collar19 in screw threaded engagement with the spindle l9. When the collar 19is screwed downwardly, the collet TI is compressed so that the tool 15may be removed. A protecting snap cover 80 may be provided for u thelower end of the porcelain 42, fitting in the bore of the lapping tool15.

In order to prevent rotation of the brushes 28, 29, 30 and 3|, the upperpart of the insulating rod 32 is attached to a metal rod 8?. whichpasses through a bore in the stationary journal portion lll'of the drillpress. This rodmay move up and down in the portion III as the tool isused. A suitable casing 85 of insulating material may be provided tocoverthe rings 24 to 21, the brushes 28, to 3|, and adjacent parts ofthe apparatus, as shown.

Referring now to Figure 4, the operator first sprinkles the lappingpowder to be used on a steel plate 86 and rolls the lap 15 in thispowder. Anysuitable abrasive may be used, for example alumina in itsvarious forms, including electric furnace fused alumina: emery andcorundum, also silicon carbide or other hard carbides including boroncarbide. Preferably for lapping certain hard steels, diamond dust may beused. When the tool 15 has been rolled in the powder for a short period,it is charged with abrasive and then the tool may be assembled as shownin Figure 1. By means of the switch 80 and rheostat ll, the operatorheats the tool which he first 1 lowers intothe work piece, using thehand wheel or lever of the drill press, not shown. The operator may thenreciprocate the tool vertically in the bore of the work piece while itrotates therein. The controls should be used to heat the tool upgradually. As the tool heajis, it expands and, therefore, becomes ofgreater diameter. Its size is proportional to the temperature and thetemperature can be deduced from the reading of the ammeter III which, infact, may be calibrated in terms of temperature or even in terms ofhundred thousandths of an inch above or below a certain standarddiameter.

With this apparatus very delicate lapping operations can be performed,since a few degrees rise of temperature involves an exceedingly smallincrease in diameter of the lapping tool. The operation can be carriedon rapidly since the tool I5 will heat up rapidly when the rheostat I8is operated and when the current is cut off, the tool cools down rapidlyowing to the fact that it is made of metal. Also, it can be removed fromthe bore of the workpiece and the rotary motion thereof sets up airfriction which rapidly cools the tool. Lapping operations which alwayshave in- Outside hollow Y volved a good deal of time may thus be carriedout according to the present invention relatively expeditiously.

The object to be lapped will usually comprise a piece of steel of somesize which may be heldin a suitable clamp or holder, not shown. This mayalso be of metal and thus heat will be rapidly conducted away from theobject to be lapped. Various expedients may be adopted for the coolingof the object to be lapped, if desired, such as theuse of a stream ofwater which need not be directed into the bore to be lapped but onlyagainst the outside of the article. In this manner, control over thelapping operation can more readily be effected. Also, an air jet can -beused and is very effective to prevent the object being lapped fromheating up due to the heat from the lap.

It will thus be seen that there has been provided by this invention anapparatus and a method in which the various objects hereinabove setforth together with many thoroughly practical advantages aresuccessfullyachieved. As many possible embodiments may be made of themechanical features of the above invention and as the art hereindescribed might be varied in various parts, all without departing fromthe scopeof the invention, it is to be understood that all matterhereinbefore set forth or shown in the accompanying drawing is to beinterpreted as illustrative and not in a limiting sense.

I claim:

1. The method of lapping to fine precision limits the bore of an articlewith an internal lapping tool substantially fitting the bore whichcomprises heating the tool from the inside thereof while in the bore ofthe article, and moving the tool in the bore while it is heated.

2. The method of lapping to fine precision limits the bore of an articlewith an internal lapping tool substantially fitting the bore whichcomprises heating the tool from the inside thereof while in the bore ofthe article, movingthe tool inthe bore while it is heated, anddetermining the temperature of the lapping tool from time to time togauge the lapping operation.

3. The method of lapping to fine precision limits the bore of an articlewith an internal lapping tool substantially fitting the bore whichcomprises heating the tool from the inside while in the bore of thearticle, moving the tool in the bore while it is heated, and'at the sametime cooling the article to an extent sufficient to prevent large riseof temperature thereof.

4. The method of lapping to line precisionlimits the bore of an articlewith an internal lapping tool substantially fitting the bore whichcomprises heating the tool from the inside while rotating it in the boreof the article, at the'same time cooling the article to an extentsuflicient to prevent large riseof temperature thereof, and determiningthe temperature of the lapping tool from time to time to gauge thelapping operation.

5. Lapping apparatus. including a cylindrical lapping tool rotatablymounted having a cylindrical lapping surface fitting the bore of a workpiece, electric resistance wire in the inside of said tool, electricconnections including rings and brushes to pass electric current throughthe resistance wire, thereby to heat the tool, and means to measure thetemperature of the tool, thereby accurately to control a lappingoperation.

6. Lapping apparatus including a cylindrical lapping tool rotatablymounted having a cylindrical lapping surface fitting the bore of a workpiece, electric resistance wire in the inside of said tool, electricconnections including rings and brushes to pass electric current throughthe resistance wire, thereby toheat the tool, and a. couple in the toolto measure the temperature thereof.

'7. Lapping apparatus including a cylindrical lapping tool rotatablymounted having a. cylindrical lapping surface fitting the bore of a workpiece, electric resistance wire in the inside of said tool, electricconnections including rings and brushes to pass electric current throughthe resistance wire, thereby to heat the tool, a couple in the tool tomeasure the temperature thereof, electric connections including ringsand brushes to take the current generated by the couple outside of thetool, and an ammet'er to measure the last mentioned current in order todetermine the temperature of the tool and thereby its size.

HERBERT S. INDGE.

